Laser scanners that operate in accordance with a propagation time measurement principle are nowadays used in many areas; they determine the propagation time of the laser beam and reflection thereof at a body penetrating the scanning fan in order to conclude the spatial position of the body from this and from the radiation angle of the laser beam. Here, the laser beam is either pulsed or is a modulated continuous laser beam; a laser beam pulse sequence of this type or the modulated continuous laser beam is usually pivoted in terms of its direction by a rotating mirror, whereby the laser beam scanning fan is formed.
For object protection it is known to mount laser scanners of this type on the object itself and/or on posts arranged in front of the object, wherein the scanning fans of said laser scanners are oriented down in a straight line or at an incline relative to the ground. A body, as it penetrates the scanning fan, can thus be detected on account of the reflection of said body; however, devices of this type, if the object to be protected has a very complex outline, require a very high number of laser scanners and of course can be flown over very easily.
A laser monitoring arrangement comprising a laser transmitter that rotates on a mast high above the object to be protected and at the same time emits laser beams downwardly three-dimensionally in the shape of a cone in order to monitor the space around the object for penetrators is known from EP 0 532 976 A1. It goes without saying that in this case only a very low spatial and/or temporal resolution can be obtained, since, in particular in the case of relatively large objects, for example in the case of object protection for power plants, the monitored space is very large. In order to attain an improved resolution, a multiplication of the user laser transmitters is only possible to a very limited extent, however, since with a high number of laser transmitters a correct assignment of the current reflections occurring in any case at the ground is now practically impossible; in addition, the structural outlay for an arrangement of this type comprising a multiplicity of laser transmitters and the mast supporting said transmitters would be very high.